There have been multiple reports of users that paid via PayPal but their account was not upgraded.

It’s very frustrating if you trust someone your money and nothing happens. We totally understand and we apologize!

We’ve found that unfortunately there can be delays at PayPal. Sometimes the instant payment notifications that our system needs to get to finalize the upgrade are sent minutes after the payment. We need these within seconds for a smooth upgrade.

These kind of delays are very bad for your workflow and your trust in our system. We’ve signalled this issue at PayPal with high priority. They are now investigating but unfortunately there seems to be no easy fix.

If you have paid with PayPal but your upgrade is not coming through, please get a cup of coffee and wait a couple of minutes. You may also try to log off and on again.

PayPal has announced the problems are system wide, not specific for our application:

06/08
Thursday
Unscheduled
06/08/17 08:00 AM to ongoing
PayPal Notifications
Live Site Status Update
Notification: We are experiencing a system issue which may be affecting different functionalities on the PayPal Live Site. Please see the details below.

Some Instant Payment Notifications (IPN) may be delayed
Some email and SMS notifications may be delayed
Some transactions may be missing from the History page of the PayPal account and via transaction search functionality

Our technical teams have been engaged and are actively troubleshooting the issue.
Sent Jun 8, 2017 06:26 PM CEST by DBO
Start time: Jun 8, 2017 08:00 AM CEST
At this time, there is no alternative work-around.

This has also happened to us, however we paid using a credit card via the PayPal system, I have a receipt from PayPal but my account has not been upgraded with the payment. It is now over 15 minutes ago.
Can someone please assist?